DETERMINATION OF SLUMP OF PORTLAND CEMENT CONCRETE

APPARATUS

1. Slump mold – made of galvanized metal not thinner than No. 16 gage in the form of the lateral surface of the frustum of a cone with the base 203 mm ( 8 in,) in diameter, the top 102 mm (4 in.) in diameter and the height 305 mm (12 in.). The base and the top shall be open and parallel to each other and at right angles to the axis of the cone. The mold shall be provided with foot pieces and handles. A mold which clamps to a non absorbent base plate is acceptable.

2. Tamping Rod – made of a round, straight level rod 16 mm (5/8 in.) in diameter and approximately 600 mm (24 in) in length, having the tamping end rounded to a hemispherical tip, the diameter of which is 16 mm.

3. Scoop or Shovel

4. Steel Ruler

5. Container for mixing concrete sample

SAMPLE

The sample of concrete from which test specimens are made shall be representative of the entire batch. It shall be obtained in accordance with Method in Sampling Fresh Concrete.

PROCEDURE

1. Dampen the mold and place it on a flat, moist, nonabsorbent surface. Held firmly in place during filling by the operator standing on the two foot pieces. From the sample of concrete obtained, immediately fill the mold in three layers, each layer approximately one third the volume of the mold. In placing each scoopful of concrete move scope around the top edge of mold as concrete slides.

2. Rod each layer with 25 strokes of the tamping rod, distributed uniformly over the cross-section of each layer. The rod should penetrate the entire depth of the layer being tamped. Rod the second layer and the top layer each throughout its depth, so that the strokes just penetrate into the underlying layer.

3. In filling and rodding the top lay, heap the concrete above the mold before rodding is started. If the rodding operation results in subsidence of the concrete below the top edge of the mold, add additional concrete to keep an excess of concrete above the top of the mold at all times. After the top layer has been rodded, strike of the surface of the concrete by means of a screeding and rolling motion of the tamping rod.

4. Remove the mold immediately from the concrete by raising carefully and slowly in a vertical direction. Raise the mold a distance of 300 mm (120 in) in 5+ 2S by a steady upward lift with no lateral motion. Complete the entire test from the start of the filling through removal of the mold without interruption and complete it within an elapsed time of 2-1/2 minutes.

4. Measure immediately the slump by determining the vertical difference between the top of the mold and the displaced original center of the top surface of the specimen.

CALCULATION

1. Record the slump in terms of millimeters to the nearest 6mm (1/4 in.) of subsidence of the specimen during the test.

Slump = 305 – millimeter of height after subsidence.

SAMPLING FRESH CONCRETEA. SAMPLING

1. The elapsed time between obtaining the first and final portions of the composite samples shall be as short as possible, but in no instance shall it exceed 15 minutes.

2. Transport the individual samples to the place where fresh concrete tests are to be performed or where test specimens are to be molded. They shall then be combined and remix with a shovel the minimum amount necessary to ensure uniformity and compliance with the minimum time limits specified in no 3.

3. Start tests for slump or air content, or both, within 5 min after obtaining the final portion of the composite sample. Complete the tests as expeditiously as possible. Start molding specimens for strength tests within 15 min after fabricating the composite sample. Keep the elapsed time between obtaining and using the sample as short as possible and protect the sample from the sun, wind, and other sources of rapid evaporation, and from contamination.

B. PROCEDURE

1. Size of Sample – Make the samples to be used for strength tests a minimum of 28 liters (1 ft3). Smaller may be permitted for routine air content and slump tests and the size shall be dictated by the maximum aggregate size.

2. The procedures used in sampling shall include the use of every precaution that will assist in obtaining sample that are truly representative of the nature and condition of concrete sampled as follows:

a) Sampling from Stationary Mixers, except Paving Mixers.

Sample the concrete at two of more regularly spaced intervals during discharge of middle portion of the batch. Take the samples, so obtained within the time limit specified in section A, and blend composite them into one composite sample for test purposes. Do not obtain samples from the very first or last portion of the batch discharge. Perform sampling by passing a receptacle completely through discharge stream, or by completely diverting the discharge into a sample container. If discharge of the concrete is too rapid to divert the complete discharge stream, discharge the concrete into a container or transportation unit sufficiently large to accommodate the entire batch and then accomplish the sampling in the same manner as given above. Take care not to restrict the flow of concrete from the mixer, container, or transportation unit so as to cause segregation. These requirements apply to both tilting and non tilting mixers.

b) Sampling from Paving Mixers

Sample the concrete after the contents of the paving mixer have been discharged. Obtain samples from at least five different portion s of the pile and then composite into one sample for test purposes. Avoid contamination with subgrade materials or prolonged contact with an absorptive subgrade. To preclude contamination or absorption by the subgrade, sample the concrete by placing three shallow containers on the subgrade and discharging the concrete across the container. Composite the samples so obtained into one sample for test purposes. The container shall be of a size sufficient to provide a composite sample size that is in agreement with the maximum aggregate size.

c) Sampling from Revolving Drum Truck Mixers or Agitators

Sample the concrete at two of more regularly spaced intervals during discharge of the middle portion of the batch. Take the sample so obtained within the time limit specified in Section A and blend the, into one composite sample for test purposes. In any case do not obtain samples until after all of the water has been added to the mixer; also do not obtain samples from the very first or last portions of the batch-discharge. Sample by the repeatedly passing a receptacle through the entire discharge stream or by completely diverting the discharge into a sample container. Regulate the rate of discharge of the batch by the rate of revolution of the drum and not by the size of the gate opening.

d) Sampling from Open-Top Truck Mixers, Agitators, Non-agitating Equipment, or other types of Open-Top containers.

Take samples by whichever of the procedures described in Sections a, b or c is most applicable under the given conditions.

DETERMINATION OR AIR CONTENT OF FRESHLY MIXED CONCRETEBY THE PRESSURE METHOD

APPARATUS

1. Air Meter – consisting or measuring bowl and cover assembly (see Fig. 1) with working pressures of 51 to 207 kPa (7.5 to 30 psi).

2. Measuring Bowl – cylindrical in shape and made of steel having a minimum diameter equal to 0.75 to 1.25 times the height and a capacity of at least 0.006m3 (0.20 ft3).

3. Cover Assembly - made of steel and constructed to provide for a pressure-tight between bowl and cover assembly. The dial of the pressure gage shall be calibrated to indicate the percent of air and the graduations shall be provided for a range in air content of at least 8% easily readable to 0.1%. A suitable hand pump shall be provided with the cover either as an attachment or as an accessory

4. Trowel – A standard brick mason’s trowel.

5. Tamping Road –6. Mallet- A mallet (with a rubber of rawhide head) weighing approximately 1.25± 0.50 lb

(0.57 ± 0.23 kg) for use with measures of 0.5 ft7. Mallet – A mallet (with a rubber or rawhide head) weighing approximately 1.25 + 0.50 lb

(0.57+ 0.23 kg) for use with measures of 0.5 ft3 (14 dm3) or smaller and a mallet weighing approximately 2.25+0.50 lb (1.02+0.23 kg) for use with measures larger than 0.5 ft3.

8. Strike-off Bar – A flat straight bar or steel or other suitable metal.

9. Funnel, - with the spout fitting into spray tube.

10. Measure for water, having the necessary capacity to fill the indicator with water the top of the concrete to the zero mark.

11. Vibrator

12. Sieve, 1 ½ in. (37.5 mm) with not less than 2 ft2 (0.19 m2) of sieving.

PREPARATION OF CONCRETE TEST SAMPLE

Obtain the sample of freshly mixed concrete in accordance with sampling Fresh Concrete (AASTHO T 141). If the concrete contains coarse aggregate particles that would be retained on a 2-in. (50 mm) sieve, wet-sieve a sufficient amount of the representative sample over a 1 ½ in (3.75 mm) sieve to yield somewhat more than average materials to fill the measuring bowl of the size selected for use. Carry out the wet-sieving operation with the minimum practical disturbance of the mortar. Make no attempt to wipe adhering mortar from coarse aggregate particles retained on the sieve.

PROCEDURE

1. Place the representative sample of fresh concrete in the measuring bowl in three layers of approximately equal volumes. Consolidate each layer of concrete by 25 strokes of tamping rod evenly distributed over cross-section. In rodding, the rod should penetrate the entire depth of the layer being tamped. After each layer is rodded, tap the sides of the measure smartly 10 to 15 times with the mallet to close any voids left by the tamping rod. Strike-off the top surface by sliding the strike-off bar across the top flange or rim of the measuring bowl until the bowl is just level full.

2. Thoroughly clean the exterior of measuring bowl to remove all excess concrete and clump the cover assembly to the measuring bowl in a pressure-tight seal. Close the air valve between the air chamber and the measuring bowl and open both petcocks on the holes through the cover. Using a rubber syringe, inject water through one petcock until water emerges from opposite petcock. Jar the meter gently until all air is expelled from the same petcock.

3. Close the airbleeder valve on the air chamber and pump air into the air chamber until the gage hand at the initial pressure line by pumping as necessary, tapping the gage lightly. Close both petcocks on the holes through the cover. Open the air valve between the air chamber and measuring bowl. Tap the sides of the measuring bowl sharply to relieve local restraints. Lightly tap the pressure gage to stabilize the hand and read the percentage of air on the dial of the pressure gage. Release the pressure by opening both petcocks before removing the cover.

CALCULATION

The percentage of air content on freshly mixed concrete can be obtained as the actual reading noted in the dial. If there’s a doubt in the result of test, correction factor of aggregate, used shall be determined by subtracting its value to the actual reading obtained in the meter.

DETERMINATION OF WEIGHT PER CUBIC METER YIELD AND AIR CONTENT(GRAVIMETRIC) OF CONCRETE

APPARATUS1. Balance – accurate to within 0.3% of the test load at any point within the range use.

2. Tamping rod – a round, straight steel rod, 16mm in diameter and approximately 600mm, in length, having the tamping end rounded to a hemispherical tip the diameter of which is 16mm.

3. Measure - a cylindrical container made of metal, watertight and sufficiently rigid to retain its form and calibrated volume under rough usage. The top rim of the air meter bowls shall be smooth and plane within 0.01 in. (0.25).

4. Strike-off Plate – a flat rectangular metal plate at least 6mm thick with a length and width at least 50mm greater than the